This invention relates to mechanical disc brakes and, particularly to mechanical disc brakes of a floating caliper type having an adjusting mechanism for compensating for wear of friction pads as shown, for example, in U.S. Pat. Nos. 4,088,204 and 4,162,720.
Conventional mechanical disc brakes comprise a force converting mechanism converting rotational input force applied through a cable associated with a brake pedal or a brake lever into a linear thrust force which is applied to one of two opposing friction pads. The mechanism usually comprises a lever connected to the cable, a nut integrally connected to the lever, a ramp plate having an inclined groove, and a ball interposed between the nut and the ramp plate and engaging with the inclined groove. A rod engages with the nut and abuts with the one friction pad. When the nut is rotated by the lever, the nut is displaced in the axial direction with respect to the ramp plate; the displacement of the nut is transmitted to the one friction pad through the rod; and the reaction force is transmitted to the other opposing friction pad through the caliper, thereby clamping the disc between the friction pads. When the force applied through the cable is released the rod retracts by a return spring.
The screw-thread engagement between the rod and the nut constitutes the adjusting mechanism for compensating for the wear of the friction pads. By threadingly rotating the rod with respect to the nut and toward the friction pad, the wear of the friction pads can be compensated for.
The relative rotation of the nut and the rod can be effected manually or automatically. For automatic adjusting, a ratchet mechanism is provided between the nut and the rod.
The relative rotation between the nut and the rod must be prevented for maintaining the adjusted position. It is possible to maintain the adjusted relative position between the nut and the rod by increasing the frictional resistance in the screw-threads between the nut and the rod. However, there is usually provided for this purpose a rotation control member between the rod and the nut or between the rod and the caliper.
It is necessary to prevent the change in the spring force of the return spring which would be caused by such effects as vibrations; and further, it is required to maintain the spring force of the return spring constant irrespective of the relative displacement of the rod with respect to the nut.